Glycerol kinase (GK) catalyzes the entry of glycerol into the glucose and triglyceride metabolic pathway. Impaired glucose tolerance (IGT) and hypertriglyceridemia are associated with an increased risk of diabetes mellitus (DM) and cardiovascular disease. The relationship between glycerol and the risk of IGT, however, is poorly understood.
Work described herein details the identification of alterations in the glycerol kinase (GK) gene which result in severe hyperglycerolemia and impaired glucose metabolism and body fat distribution. Glycerol levels are shown to be highly heritable and associated with significant variations in glucose tolerance. This work indicates that glycerol is a potentially significant predictor of the magnitude of glucose tolerance and thus of increased risk of diabetes mellitus (DM) and cardiovascular disease.
Work described herein assessed the association of fasting plasma glycerol concentration with 2-hour glucose following a 75 g oral glucose tolerance test in a cohort of 1056 unrelated French Canadians presenting with a family history of hypertriglyceridemia. The familial resemblance of fasting glycerol in these subjects"" families has been estimated, and the GK gene was screened for the presence of mutations.
Family screening in the initial cohort identified 18 individuals with severe hyperglycerolemia (values above 2.0 mmol/L). These individuals were shown to carry a missense mutation (N288D) in exon 10 of the GK gene. Analysis of the biological variables among the N288D carriers led to the observation that variation in glycerolemia was a predictor of impaired glucose metabolism and of abdominal fat accumulation. In the absence of severe hyperglycerolemia, a significant familial resemblance for fasting glycerol concentration (F ratio:6,3; p less than 0.0001) was observed. Furthermore, multivariate analyses performed in the initial cohort revealed substantial variation in fasting glycerolemia which was associated with significant differences in glucose tolerance, independent of known covariates such as age, gender and body mass index as well as fasting triglyceride, glucose, insulin and free fatty acid concentrations. These results suggest an important genetic connection between glycerol and glucose homeostasis and indicate that assessment of glycerol levels could be a clinically useful tool in the prediction of IGT.
The invention relates to a method of predicting or assisting in the prediction of impaired glucose tolerance, diabetes mellitus, hyperglycerolemia and/or cardiovascular disease in an individual, comprising the steps of obtaining a biological sample from an individual; and assessing the glycerol level in said sample, wherein an increased level of glycerol in said sample as compared with a control sample is predictive of impaired glucose tolerance, diabetes mellitus, hyperglycerolemia and/or cardiovascular disease in the individual. In one embodiment, the increased glycerol level is greater than about 0.08 mmol/L. In another embodiment, the biological sample is a blood sample. In one embodiment, the glycerol level is a plasma glycerol level, and in one embodiment the sample is a fasting sample.
The invention also relates to a method of predicting or assisting in the prediction of impaired glucose tolerance, diabetes mellitus, cardiovascular disease and/or hyperglycerolemia in an individual, comprising the steps of obtaining a nucleic acid sample from an individual; and determining the nucleotide present at nucleotide position 29 of exon 10, wherein presence of a guanine at said position is predictive of impaired glucose tolerance, diabetes mellitus, cardiovascular disease and/or hyperglycerolemia in the individual as compared with an individual having an adenosine at said position.
The invention also relates to a method of predicting or assisting in the prediction of impaired glucose tolerance, diabetes mellitus, cardiovascular disease and/or hyperglycerolemia in an individual, comprising the steps of obtaining a biological sample comprising the glycerol kinase protein or portion thereof from an individual; and determining the amino acid present at amino acid position 288, wherein presence of an aspartate at said position is predictive of impaired glucose tolerance, diabetes mellitus, cardiovascular disease and/or hyperglycerolemia in the individual as compared with an individual having an asparagine at said position.
The invention further relates to a method of identifying an agent which is an agonist of glycerol kinase, comprising the steps of providing a recombinant host cell of the invention; contacting said host cell with an agent to be tested; and assessing the ability of the agent to increase glycerol kinase activity, wherein an agent which increases glycerol kinase activity is an agonist of glycerol kinase activity. In one embodiment, the step of assessing is performed by determining the level of one or more downstream effects of a glycerol metabolic pathway and comparing said level with a level in an appropriate control.
The invention further relates to a method of predicting or assisting in the prediction of impaired glucose tolerance, diabetes mellitus, cardiovascular disease and/or hyperglycerolemia in an individual, comprising the steps of obtaining a biological sample from an individual; and assessing the level of glycerol kinase gene expression in said sample, wherein a decreased glycerol kinase gene expression level in said sample as compared with a control sample is predictive of impaired glucose tolerance, diabetes mellitus, cardiovascular disease and/or hyperglycerolemia in the individual.
The invention also relates to a method of predicting or assisting in the prediction of impaired glucose tolerance, diabetes mellitus, cardiovascular disease and/or hyperglycerolemia in an individual, comprising the steps of obtaining a biological sample from an individual; and assessing the level of active glycerol kinase in said sample, wherein a decreased level of active glycerol kinase in said sample as compared with a control sample is predictive of impaired glucose tolerance, diabetes mellitus, cardiovascular disease and/or hyperglycerolemia in the individual.
The invention also relates to an isolated nucleic acid molecule comprising SEQ ID NOS: 1-4. The invention further relates to an isolated nucleic acid molecule comprising a portion of SEQ ID NOS: 14, wherein said portion is at least 10 nucleotides in length and wherein said portion comprises a polymorphic nucleotide position occupied by the alternate (non-wildtype) nucleotide. The invention also relates to nucleic acid constructs and recombinant host cells comprising the isolated nucleic acid molecules of the invention. For example, the recombinant host cell can be selected from the group consisting of adipocytes, lymphoblasts and fibroblasts.
The invention further relates to gene products, e.g., mRNA or polypeptides, encoded by the nucleic acid molecules of the invention.